JPH04112525A - Direct drawing method - Google Patents

Abstract

PURPOSE:To execute a direct drawing operation with good accuracy while a mode changeover operation is being executed repeatedly by a method wherein, by means of a conversion matrix 'M', a block position whose detection is anticipated in another mode is found by using the shape of a block mark detected in one mode. CONSTITUTION:Regarding a reference mark near a corner in a subfield deflection region, the position of the reference mark at the corner of a subfield is found in a reference mode while a total of five points, i.e., four points and the center, are detected. Then, a mode is changed; the position of a reference mark at a corner of the same subfield is found in the same manner. When the position is compared with the result of the reference mode, it is possible to find the shift amount and the magnification of the subfield. The result (matrix) which has been found is stored in a control part 1. It is decided whether a correction is required or not by the command of a CPU. It is operated as a data which has been converted by an electrostatic absolute calibration factor 2. The shift amount in the center of a block in each mode is stored in a shift 3; it is added to an electrostatic data by the command of the CPU after a mode has been corrected. The discrepancy amount of the drift of a beam position is corrected as required by measuring the reference mark.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a direct lithography method in an electron beam lithography apparatus.

[Conventional technology]

Electron beam writing equipment using a Gaussian beam has the contradictory goals of high throughput and fine writing by keeping the exposure current density almost constant, using a large beam for large-area patterns, and using a large beam for fine patterns. I) There is an apparatus whose electron optical system is designed so that drawing can be performed using a small beam diameter.

Furthermore, with this device, it is also possible to use a correction method called contour decomposition to correct the proximity effect, which is a problem for electron beam lithography devices.

Specific optical systems include those that change the reduction ratio of a plurality of condenser lens systems while keeping the excitation conditions of the objective lens constant, and those that change the reduction ratio of the objective lens. Hereinafter, changing the beam diameter is defined as changing the mode.

Conventional devices do not have a good method for performing direct drawing while changing modes. Therefore, in order to change the mode in direct writing, it is necessary to first write the entire surface of the wafer in a certain mode, then change the mode and write the entire surface of the wafer again. However, in mode conversion, the added value of origin correction called beam position drift correction has no relationship between modes, so it may deviate greatly in the opposite direction, and beam position drift correction often fails after mode switching. For this reason, it was necessary to artificially replace the beam drift value with zero when changing the mode, and then start drawing again.

[Problem to be solved by the invention]

The above conventional technology has the following problems: in direct writing, the beam position drift value must be replaced with zero when the mode is changed, the mode must be changed frequently, and the shape of the writing area is corrected by detecting chip marks when changing the mode. There is no consideration given to the number of chip mark detections and the increase in drawing time, etc., and the mode cannot be changed frequently, and human intervention is required to change the mode. There was a problem that the drawing time increased.

The present invention provides an electron beam with a direct writing method that allows frequent mode changes in direct writing, does not require human intervention to change modes, and has approximately the same writing time as writing in one mode. The purpose of the present invention is to provide a drawing device.

[Means to solve the problem]

To achieve the above objective, a transformation matrix is used that bridges multiple corrections of electron beam deflection distortion between modes. The matrix was determined so as to be able to correct up to the trapezoidal term required for direct writing. The matrix includes information such as the shift amount of the block center, the shift amount of the subfield center, and the magnification change of the subfield. The matrix is stored in a register, and the matrix is recalled in accordance with the mode conversion, and the deflection correction coefficient of the reference mode and the matrix are calculated.

In mode conversion, the drawing data is converted according to the calculation result of the matrix. As a result, the deflection plate receives data whose deflection distortion and drawing position have been corrected. Furthermore, since correction is performed without detecting block marks each time the mode is converted, the objectives of high accuracy and speed are met.

[Effect]

With the transformation matrix tty1'', it is possible to use the shape of a block mark detected in one mode to find the position of a block expected to be detected in another mode.

Therefore, even if the mode is changed during direct drawing, drawing can be continued without redetecting block marks, and changes in block position due to mode changes can be corrected correctly. Direct drawing can be performed with high precision while repeatedly switching modes. Further, since the block mark is not redetected, the drawing time can be completed in almost the same time as the drawing result in one mode.

〔Example〕

An embodiment of the present invention will be described below. FIG. 1 shows an electron optical system of the present invention. 1 is a Ti/W cathode. The electron beam generated from the cathode is accelerated by the electrostatic lens 2,
A crossover (virtual light source) is created on the blanking abutment 4 by the converging lens 3a, and the objective abutment 5 is irradiated. Of the irradiated electron beam, the electron beam that has passed through the objective aberthier 5 is converged by the objective lens 6 and focused on the stage sample surface 7. The excitation of the convergent lens 3a is set to 0, and the excitation of the convergent lens 3b at a different position is activated.
Hereinafter, like the electron beam described above, after creating a crossover on the planking aperture 4, the electron beam is focused on the stage sample surface 7. In this way, the converging lenses 3a, 3
By selectively using either one of them, two magnifications of the electron optical system can be obtained, and beam diameters of different sizes can be obtained with substantially constant current density. At this time, the objective lens 6
The object point and image point of are blanking Avatia 4, respectively.
．． Since they are the same on the stage sample surface 7, the excitation conditions of the objective lens 6 do not change by switching the converging lens.

However, the deflection distortion for the deflection system 8 within the objective lens 6 changes. It is a convergent lens 3a +, 3b
The optical axes of the two do not match due to errors in manufacturing, assembly, and installation. For this reason, even if the focus is set at the same position on the stage sample surface 7 by switching the converging lenses 3a and 3b, the positions of the crossovers formed in the blanking aberrations 4 cannot be made at the same position. In other words, the optical axis is misaligned with respect to the deflection system. For this reason, the converging lens 3a.

Each time 3b (mode) is switched, distortion caused by deflection must be corrected. In the case of direct writing, even if deflection distortion correction is ideal, error factors such as wafer loading errors and wafer expansion/contraction due to process effects occur. Therefore, it is necessary to match the drawing to the base of the wafer. Actually, the wafer base shown in Figure 2,
The above error factors are corrected using wafer mark 1 and block mark 2 as reference marks. That is, the wafer mark is detected, the wafer loading error is corrected, the expected target block center position is determined, the block is moved to the block mark position, the four marks are detected, and the actual block shape is determined. By the way, in a step-and-repeat drawing device, drawing data is field and subfield data X+ Ye X+
3', and the shapes of the fields and subfields are adjusted to match the shape. Specifically, the following formula is used. However, child A and B+ (i=o~3) are obtained from the block mark detection results, and al, tz (i=o~3) are
A1. It can be determined from Bt.

In the above direct drawing, when the mode is switched, the block shape does not change, but the field.

Since the subfield shape changes, the shape does not match the block shape. Furthermore, the block center position may shift by several μm before and after mode switching. Therefore, some kind of correction is required to improve accuracy. Furthermore, the magnification is not necessarily the same between modes. fact,
When measuring the shape of subfields using electrostatics, the center and subfield sizes differ between modes. Therefore, the appearance of the standard mark that serves as a reference mark differs between modes. Subfield calibration is based on the design dimensions of the reference mark, so in order to improve subfield connection accuracy, it is necessary to i) "determine and correct the shift amount and magnification of the subfield center between modes" Become.

FIG. 3 shows a correction logic configuration for direct writing according to the present invention.

j), a total of 5 points, including 4 reference marks 2 near the 1st corner of the subfield deflection area shown in Fig. 4, are selected.
Detect the point and use the reference mote to find the reference mark position of the subfield corner. Next, by changing the mode and similarly determining the reference mark position at the same subfield corner and comparing it with the result in the reference mode, the shift amount and magnification of the subfield can be determined. The obtained result (matrix) is
The data is stored in the control unit ~1, and the presence or absence of correction is determined under the instruction of the CPU, and the data is calculated using the electrostatic absolute calibration coefficient ~2.

Prior to direct drawing, ii) "Absolute calibration is performed, and the absolute calibration uses the absolute calibration results of the reference mode to measure the deflection distortion of each change mode, determines correction so that the distortion is corrected, and stores it in a table. .'' Absolute calibration after changing the mode can be quickly and easily obtained by calculating the absolute calibration result of the reference mode and the calculated correction coefficient.

When (i) was corrected using the results of (i), field and subfield distortions could be correctly corrected before and after mode switching.

After this, block marks are detected and alignment correction is performed, but it is necessary to solve problems associated with the mode change. That is, correction of the shift amount of the block center and beam position drift. The shift amount of the block center is determined by detecting the wafer mark in each mode, calculating the block center in each mode, storing it in a register, and calling the register corresponding to the mode as necessary. Can be corrected. Specifically, the shift amount of the block center in each mode is stored in shift ~3, c
Under the command of pu, it is added to the electrostatic data after mode correction. Furthermore, the beam position drift may be determined by measuring the reference mark and correcting the amount of deviation, if necessary.

〔Effect of the invention〕

According to the present invention, the shape of a block mark detected in one mode can be used to determine the block position and shape expected to be detected in another mode, down to the trapezoidal term. Even if it is repeated, it can be performed accurately without causing any deviation in the drawing position.

Furthermore, since block mark detection does not have to be performed every time the mode is switched, the drawing time is approximately the same as drawing in one mode.

Furthermore, since beam position drift is not detected by mode switching, no human intervention is required.

Furthermore, since mode conversion is possible, it has become possible to efficiently correct the proximity effect, which is a problem for electron beam lithography equipment, using a correction method called contour decomposition.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the electron optical system of the present invention, Fig. 2 is a diagram showing the stage (laser) coordinate system, Fig. 3 is a diagram showing the correction logic configuration of direct writing of the present invention, and Fig. 4 is a diagram showing the measurement FIG. 3 is a diagram showing a comparison of results. 1... Cathode, 2... Electrostatic lens, 3a, 3b...
Converging lens, 4...Blanking aberthia, 5...
- Objective abutment, 6... Objective lens, 7... Stage sample surface. Figure 1 Figure 2 Stage (Ras)an 1 Masako

Claims (1)

[Claims] 1. Measure chip marks using a plurality of modes, calculate the shape of a drawing area from the measured values using an electronic computer, store the calculated data in a matching table, and store the calculated data in a table according to the combined data. A direct drawing method for performing drawing, characterized in that a conversion matrix between modes is used. 2. The direct writing method according to claim 1, wherein the plurality of modes are modes in which the magnification of the charged particle optical system is changed by changing the magnification of the converging lens system without changing the excitation of the objective lens. 3. In an electron beam lithography system having a function of measuring a chip mark, calculating the shape of a lithography area from the measured value using an electric computer, and storing the calculated data in a table,
An electron beam lithography apparatus comprising means for calculating the transformation matrix according to claim 1, a function of selecting the matrix as required and storing it in a table, and a function of performing calculations on the table and the combination table. . 4. The electron beam lithography apparatus according to claim 3, wherein the transformation matrix according to claim 3 is based on the mode according to claim 2. 5. The electron beam lithography apparatus according to claim 1, which has a function of determining and storing a beam shift value in advance in accordance with a mode change, and a function of selecting the value as necessary; An electron beam lithography apparatus characterized in that a beam is deflected based on a value stored in a register.